1. Field of the Invention
The present invention relates to a transmission shaft for transmitting rotational movements and/or forces, also commonly called a torque shaft. The invention also relates to a method for manufacturing such a shaft.
The field of the invention is more particularly that of shafts made from composite materials. In a known manner, such a composite shaft comprises a body made from a plastic matrix, in particular a thermoplastic or thermosetting resin, incorporating mechanical strengthening elements, in particular fibers.
2. Brief Description of the Prior Art
This type of shaft is used in the aeronautic and automobile industries to support different functional mechanical assemblies, actuated or stressed during the rotation of the shaft. For example, such a shaft can be used to deploy the leading edge and trailing edge flaps of airplane wings, so as to increase the lift thereof, or to orient the airplane door latches, so as to make it possible to open and close those doors. According to another example, such a shaft can constitute an automobile steering column.
In practice, to avoid deteriorating the composite material of the body, the aforementioned mechanisms are not directly supported by the bodies, but by metal tubular inserts secured to the longitudinal ends of the body and providing the mechanical connection between the body and the mechanisms, such as in U.S. Pat. No. 4,681,556 for example. However, during the torsion of the shaft, and therefore the transmission of forces by the insert between the body and the mechanisms, the shaft undergoes major stresses in an interface area between each insert and the body. These stresses in particular include a shearing component and, over an extended period of time, can cause a deterioration of the plastic matrix in the interface area with the insert.
Furthermore, following their manufacture, certain torque shafts have a reduced quantity of fibers in the interface area between the body and the insert(s), so that a weakening of the shaft during operation can be observed in that area.